Gas distribution systems, in particular natural gas distribution systems, typically transport gas from a producer to a consumer along a series of pipes and through a series of valves. Each gas distribution system may include one or more regulator valves that control the pressure of the gas within the distribution system. Normally, the gas is transmitted at a high pressure through the system. However, the pressure of the gas must be reduced prior to final distribution to the consumers. This pressure reduction is typically accomplished at pressure reducing stations within local networks.
Typically, these pressure reducing stations include one or more pressure regulating valves and some sort of safety device to shut off the flow of gas should the pressure regulating valve fail. Most commonly, slam-shut safety valves are used for this purpose. The slam-shut safety valve is generally disposed upstream of the pressure regulating valve so that the slam-shut valve may prevent gas from reaching the pressure regulating valve in the event of a pressure regulating valve failure. The slam-shut safety valve monitors gas pressure downstream of the pressure regulating valve for maximum and minimum pressure tolerances. If the downstream pressure exceeds either the maximum or minimum tolerance, the slam-shut safety valve closes, cutting off the flow of gas to the pressure regulating valve and preventing an uncontrolled leak of gas due to the pressure regulating valve failure.
Typically, the slam-shut safety valve includes a cam having a first cam arm that is operatively coupled to a diaphragm that senses downstream pressure, thereby causing the cam to rotate about a rotational axis in response to changes in downstream pressure. The first cam arm is generally elongated, and a flexion spring is typically coupled to a distal end of the first cam arm. The flexion spring is typically formed from a single wire, and the flexion spring typically includes a wound cylindrical portion that is disposed around the distal end of the cam arm such that the longitudinal axis of the cylindrical portion is coaxial with a longitudinal axis of the elongated first cam arm. The flexion spring also includes an extended portion that outwardly extends from an end portion of the cylindrical portion in a linear direction that is parallel to the longitudinal axis of the elongated first cam arm. The extended portion typically contacts a surface disposed in the interior of the valve body. So configured, the flexion spring provides a biasing force that maintains the cam in a desired position to facilitate the rearming of the slam-shut safety valve after the slam-shut safety valve closes.